Crafting Timeless Beauty: Thermally Modified Wood in Outdoor Construction

Thermally modified wood

The preservation of wood is almost as old as wood itself.  For centuries, man has tried to preserve lumber or objects made out of wood for extended periods using different methods and techniques.  The ancient Greeks, during the rule of Alexander the Great, tried to preserve wood by soaking it in olive oil.  The Vikings charred the outside of their ships in an attempt to preserve the longevity of the wooden hulls.  The Romans wood brush a layer of tar on the outside of their ships in the hopes of extending its usual life span.  Dr. Karl Wolman, in the 1930’s, invented pressure treated lumber by infusing the lumber with various chemicals while inside of a vacuum.  Pressure treated lumber was introduced to the residential market in the 1970’s and quickly gained popularity for use in most outdoor wood applications.

Like most things in life, for every action there is an opposite reaction.  Dangerous chemicals, such as arsenic and chromium, were used in the process of manufacturing pressure treated lumber until 2004 when the U.S. Environmental Protection Agency prohibited its use due to the dangers that they presented.  Since then, companies have adapted to the changing landscape and have developed alternatives to pressure treated lumber.

One such alternative is thermally modified lumber.  Thermal modification was first scientifically documented in 1915 by a gentleman named Harry Tiemann, a kiln specialist at the Forest Products Laboratory in Madison Wisconsin.  He heated air‑dry wood in superheated steam at 150 °C, finding a reduction in hygroscopicity of the modified timber.  However, the process did not gain any measure of notoriety until the 19th Century when the technology gained popularity, with the most significant advancements coming in the 1990s led by VTT Technical Research Center of Finland.  This process was meant to bring added value to this Scandinavian country’s largest resource – wood.

Thermally modified wood

The concept of thermally modified wood is similar to the method employed by the Vikings when they charred the hulls of their longboats.  Both processes altered the chemical makeup of the lumber.  Thermally modified wood is produced in a specialized, 3‑phase kiln using only heat and steam.  Unlike pressure treated lumber, no chemicals are used.  An initial gradual increase in temperature reduces the equilibrium moisture content (EMC) of the wood.  The second phase causes a rapid spike in temperature and this is where the process begins to show its merits.  The cellular structure of the wood is altered in this high‑heat, oxygen‑deprived environment which modifies the natural acids and sugars in the lumber to prevent them from being a food source for mold, rot or fungal decay.  This process also makes the wood partially impervious to water, meaning it loses much of the natural tendency to absorb water going forward.  A natural, but unintended consequence of this process is the wood takes on a richer and dark tone similar to the look of certain exotic species.  The last phase of the process introduces steam to cool the wood down and bring the EMC back up to a suitable level.

Thermally modified wood

Unlike traditional pressure treated lumber and modern composite decking that are both fastened with screws through the top of each board, DeckWise has launched a hidden deck fastener known as ThermoClip Hidden Deck Fastener series.  These ingenious products are made from polyethylene with a stainless steel embedded insert and will not move in the diurnal temperature ranges created by the fluctuating temperatures in most climate zones.  Unlike traditional screws that bite into the wood often causing splitting, cracking and splintering on the thermally modified boards, ThermoClip Hidden Deck Fasteners are T-shaped in design and fit into grooves on the sides of each piece of decking.  These T-clips function in similar fashion to how a tongue and grove joint works.  The decking boards have the slots milled in each side typically at the lumber yard or on-site and the ThermoClip Hidden Deck Fasteners function as the tongue that are inserted into the groove in each side of the two adjacent decking boards.

ThermoClipThermoClip

The clips are held in place by #8×2” trim-head stainless steel deck screws at a 90 degree angle through the hole in the top of the clip into the joist below. The next piece of decking is then slid into place against the free edge of the clip and the same fastening process is repeated on the other side of this board.

ThermoClip Hidden Deck Fasteners come into two different colors, black and light brown to assist with camouflaging the clip between the board gaps.  They are manufactured with legs that allow for an even quarter inch spacing of the board gaps taking any guess work out of the installation process.  Unlike metal fasteners that can react with the wood, especially with pressure treated lumber, causing unsightly staining, the ThermoClip Hidden Deck Fasteners’ polyethylene outer shell does not cause any adverse reaction with the thermally modified wood.  They also have hollow legs that function as a shock-absorber of sorts providing for a more user-friendly feel that traditional rigid pressure treated decking does not offer and, the best part of all, is that they are made in America by Americans.

ThermoClip Hidden Deck Fastener

The world changes, just as aspirin was invented in 1897 to be replaced by Tylenol in 1955 which has received stiff competition from ibuprofen since its invention in 1961, pressure treated lumber, with its full complement of environmentally harmful chemicals, is being replaced by more ecologically responsible and sustainable products such as thermally modified lumber.  DeckWise, a leader of innovation in the decking industry, offers reliable fasteners that are not only highly functional but also aesthetically pleasing to the consumer.

For more info, go to Deckwise.com

Editor’s note: Images courtesy of Arbor Wood Co. www.arborwoodco.com

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